The term cement is used to designate many different kinds of materials useful as binders or adhesives. Hydraulic cements are powdered materials which, when mixed with water, form a "paste" that hardens slowly. If further mixed with sand it forms a "mortar" and if mixed with sand and coarse aggregate, such as rock, it forms a "concrete" which are rock-hard products. These products are commonly referred to as hydraulic cement mixes. Portland cement is distinguished from other cements by the different components of which it is composed, and the requirement that it meet particular standard specifications established in each country (see Cement Standards of the World, Cembureau, Paris, Fr.) For example, in the United States, the American Society for Testing and Materials (ASTM), American Association of State Highway and Transportation Officials, as well as other government agencies, have set certain basic standards for cement which are based on principal chemical composition requirements of the clinker and principal physical property requirements of the final cement mix. For purposes of this invention the term "Portland cement" is intended to include all cementitious compositions which meet the requirements of the ASTM (as designated by ASTM Specification C150), or the established standards of other countries.
Portland cement is prepared by sintering a mixture of components including calcium carbonate (as limestone), aluminum silicate (as clay or shale), silicon dioxide (as sand) and miscellaneous iron oxides. During the sintering process, chemical reactions take place wherein hardened nodules, commonly called clinkers, are formed. Portland cement clinker is formed by the reaction of calcium oxide with acidic components to give primarily tricalcium silicate, dicalcium silicate, tricalcium aluminate, and a ferrite solid solution phase approximating tetracalcium aluminoferrite.
After the clinker has cooled, it is then pulverized together with a small amount of gypsum (calcium sulfate) in a finish grinding mill to provide a fine, homogeneous powdery product known as Portland cement. Due to the extreme hardness of the clinkers, a large amount of energy is required to properly mill them into a suitable powder form. Energy requirements for finish grinding can vary from about 33 to 77 kW h/ton depending upon the nature of the clinker. Several materials such as glycols, alkanolamines, amine acetates, aromatic acetates, etc., have been shown to reduce the amount of energy required and thereby improve the efficiency of the grinding of the hard clinkers. These materials, commonly known as grinding aids, are processing additives which are introduced into the mill in small dosages and interground with the clinker to attain a uniform powdery mixture. In addition to reducing grinding energy, the commonly used processing additives listed above are frequently used to improve the ability of the powder to flow easily and reduce its tendency to form lumps during storage.
Because of the rigid compositional and physical requirements for forming suitable Portland cement clinker, clinker becomes a relatively expensive raw material. For certain applications, it is possible to substitute less expensive fillers such as limestone or clinker substitutes such as granulated blast furnace slags, natural or artificial pozzolan, pulverized fuel ash, and the like, for a portion of the clinker. As used herein, the term filler refers to an inert material that has no later age strength enhancing attributes; the term "clinker substitute" refers to a material that may contribute to long term compressive strength enhancement beyond 28 days. The addition of these fillers or clinker substitutes to form "blended cements" is limited in practice by the fact that such addition usually results in a diminution in the physical strength properties of the resultant cement. For example, when a filler such as limestone is blended in amounts greater than 5%, the resultant cement exhibits a marked reduction in strength, particularly with respect to the strength attained after 28 days of moist curing (28-day strength). As used herein, the term "blended cements" refers to hydraulic cement compositions containing between 2 and 90% more conventionally between 5 and 60%, fillers or clinker substitute materials.
Various other additives may be added to cement to alter the physical properties of the final cement. For example, alkanolamines such as monoethanolamine, diethanolamine, triethanolamine and the like are known to shorten the set time (set accelerators) as well as enhance the one-day compressive strength (early strength) of cements. However, these additives have little beneficial effect on the 28-day set strength of the finished cement and in some cases may actually diminish it. This behavior is described by V. Dodson, in "Concrete Admixtures", Van Reinhold, New York, 1990, who states that calcium chloride, the best known set-time accelerator and early-age strength enhancer reduces compressive strengths at later-ages.
U.S. Pat. Nos. 4,990,190, 5,017,234 and 5,084,103, the disclosures of which are hereby incorporated by reference, describe the finding that certain higher trihydroxyalkylamines such as triisopropanolamine (hereinafter referred to as "TIPA") and N,N-bis(2-hydroxyethyl)-2-hydroxypropylamine (hereinafter referred to as "DEIPA") will improve the late strength (strength after 7 and 28 days of preparation of the wet cement mix) of Portland cement, especially Portland cements containing at least 4 percent C.sub.4 AF. The strength-enhancing higher trihydroxyalkylamine additives described in these patents are said to be particularly useful in blended cements.
Although TIPA was able to improve the late strength properties of cement compositions, it cannot improve the early strength nor setting properties. More surprising is the observation that it tends to increase the amount of air entrained in the cement. In order to improve the early strength, setting and air entrainment properties of set cement composition containing TIPA, Myers et al taught the incorporation of known early-strength enhancers and setting accelerators, such as TEA or alkali metal salts, and known air detraining agent (ADA), such as those illustrated in U.S. Pat. No. 5,156,679.
Although the incorporation of ADA's in cement compositions containing TIPA were able to decrease the air contents, they were not able to reduce or eliminate the formation and release of bubbles from the cement compositions. This occurrence may lead to set cement compositions with large porosity and poor finished surfaces, if proper placing and finishing practices are not followed.
An additive is highly desirable which can simultaneously improve setting property, and improve strength properties at all ages, without entraining large air voids. This is desirable as it can lead to cement compositions such as Portland cement concrete with lower porosities and better finished surfaces.